Chevrolet Repair: 93 suburban noise, suburban noise, blower fan

Question
Anytime I turn on or off the ignition switch there is a knocking that comes from where the passengers feet would be. This happens if I start the engine or not. It continues for about 30 sec then stops. A/C can be on or off as well as the fan switch. I can push against where the sound is coming from and it stops. It feels like some sort of fan but I cannot access it.

Answer
Hi Rick... I tke it you mean under the dash... that is the heater box and the blower fan is in there, could be something in the box hitting fan or the fan hitting the inside of the heater box. pull the fan and see if you can see any marks in there. also check the fan for bad bushings..fan not running true...hope this helps